The present invention relates to ignition systems for internal combustion (IC) engines, and particularly to high power, high energy ignition simplified by the use of hybrid ignition features with ideal magnetic stress-balanced coils. High energy ignition is essential to the operation of IC engines using difficult-to-ignite mixtures, such as lean mixtures, high exhaust residual or high EGR mixtures, and the more difficult-to-ignite alcohol fuel mixtures. Such mixtures require hundreds of watts of igniting power and fifty millijoules or more of energy versus the ten to thirty watts and millijoules supplied by conventional ignitions. The simplified high power high energy hybrid ignition with stress-balanced coil disclosed herein can deliver the required power and energy with a minimization in the size and cost of parts to make the system practical.
The ignition disclosed is usable in the simpler distributor form or in a distributorless ignition form usable with separate leakage inductance disclosed in U.S. Pat. Nos. 5,315,982 and 5,131,376. The high power, high energy, stress-balanced minimum coil size features disclosed are based on Maxwell's equations used in conjunction with voltage doubling disclosed in U.S. Pat. No. 4,677,960 and its improvements which were first laid out in U.S. Pat. No. 5,315,982. U.S. Pat. Nos. 4,688,538, 4,774,914, 4,841,925, 4,868,730, and 5,207,208 may also be relevant to other features of the invention. The use of laminated cores for side-by-side winding coils and IGBT switches are discussed in detail in U.S. patent application Ser. Nos. 06/049,747, filed Jun. 12, 1997, and 06/063,507, filed Oct. 25, 1997.
All said above cited patents are of common assignment with this application and all include Dr. M. A. V. Ward as a sole or joint inventor. Reference to the above cited patents is sometimes made by simply listing the last three numerals of the number, as in patents '982, '376, '960, '538, '914, '925, '730, and '208. All are incorporated herein by reference as though set out at length herein.
Current capacitive discharge (CD) ignition systems are very inefficient, with typically 15% to 25% efficiency, and deliver typically only 20 to 30 millijoules (mJ) of spark energy per single spark pulse (into an industry standard 800 volt Zener load), whereas certain evidence points to a requirement of over 100 mJ of spark energy for best engine performance. In addition, CD ignition coils are typically wound with concentric primary and secondary windings to give relatively low leakage inductance for a given number of primary wire turns, which contributes to the low efficiency of the ignition system, versus the two to three times higher efficiency of 50% to 60% of the system disclosed herein.
In this application, a system is disclosed including factors such as flow resistance of the spark discharge that enables a more optimum range of leakage inductance Lpe, leakage resistance Rpe, and peak currents is for standard passenger vehicle and racing applications. Also disclosed is systems for more optimal use of the magnetic core of the coil which is achieved with side-by-side windings and judicious choice of coil winging shape and wire turns.
CD ignitions have traditionally used silicon control rectifiers (SCRs) as the main switching element controlling the discharge of the energy storage capacitors which typically have very high peak primary currents of tens of amps to over one hundred amps. Use of SCRs has the limitation of requiring full discharge of the energy storage capacitors and relatively slow restart of the power supply which recharges the capacitors. In this application is disclosed the use of insulated gate bipolar transistors (IGBTs) in conjunction with high efficiency shunt diodes and novel control circuitry to achieve controlled turn-off of the capacitor discharge process to leave some charge on the capacitors and provide rapid restart and recharging of the capacitors. The system also reduces the required size of the power supply by as much as a factor of two, especially important in high speed engine operation.
Current CD ignitions, particularly those used in racing and performance, use resonant type charging of the discharge capacitors which produces large current spikes on the battery line, as large as 20 amps in some cases, to compromise other vehicle electronic systems. On the other hand, power supplies with low ripple current are preferred, as has been disclosed in U.S. Pat. No. 5,558,071. Their operation is improved by not allowing the discharge capacitors to fully discharge as is disclosed herein.
There is therefore an advantage to improved CDI systems, both distributor and distributorless one-coil-per-plug type, which can deliver high spark energy of 100 to 250 mJ with high energy delivery efficiency of 50% to 60% (battery to spark gap efficiency). The systems preferably employ coils with side-by-side windings for low resistance and ease of manufacture. Moreover, the invention specifies the magnetics of the ignition coil and associated circuitry to make best use of the available core magnetic area and magnetic materials to achieve a more (magnetic) stress balanced condition. Also, the systems are designed to provide optimum peak spark current in terms of the best trade-off between igniting ability and spark plug erosion, as is disclosed herein.